Manufacture of self-locking nuts



y 1943- D. c. HUNGERFORD 2,318,397, I MANUFACTURE OF SELF-LOCKING NUTSOriginal Filed Sept. 10, 1938 a mi Mw w W i N v Patented May 4, 1943MANUFACTURE OF SELF-LOCKING NUTS 7 Daniel C. Hungerford, Madison, N. J.,assignor to Elastic Stop Nut Corporation,

Union City, N. J

a corporation of New Jersey Original application 1 Claim.

This application is a division of my copending application Serial#229,268 filed September 10, 1938.

The present invention relates to the manufacture of self-locking nutsand has particular reference to the manufacture of that type of self-'locking nut which when threaded on a cooperating bolt results incontinuous axial thrust exerted on the cooperating threads due toelastic flexure of a part of the nut when it is threaded onto the bolt,which thrust produces self-locking action due to maintenance of one setof flanks of the bolt and nut in continuous frictional contactingrelations with each other under the influence of the thrust produced.

It is a general object of the present invention to provide a novel andimproved method of manufacturing self-.locking nuts of the kind whichovercome the deficiencies of previous known nuts of the general typeunder consideration and which are of substantial universal applicationand to provide a novel and improved method of manufacturing such nutswhich may readily be applied in the manufacture of hardened steel nuts.

The manner in which the above general objects and other and moredetailed objects of the invention are atta ned, and the advantagesflowing from use of the novel principles of the invention, may best beunderstood and appreciated from a consideration of the ensuing portionof this specification in which, by way of example but withoutlimitation, suitable examples of nut structure made in accordance withthe invention, and the manufacture thereof are described.

In the accompanying drawing illustrative of such examples and forming apart hereof:

Fig. 1 is a central section showing nut structure made in accordancewith the invention, in

an intermediate stage of manufacture;

Fig.2 is a section similar to Fig. 1 showing a further stage ofmanufacture;

Fig. 3 is a half section showing the structure of Fig. 2 in a stillfurther stare of manufacture;

Fig. 4 is a view showing a further manufacturing step;

F g. 5 is a view show ng the completed nut applied toa bolt andillustrating the locking act on of the nut;

Fg. 6 is a side view partly in elevation and partly in section of one ofthe elements of the nut structure shown in the preceding figures;

September 10, 1938, Serial Divided August 23, 1941, Seria and thisapplication I No. 408,003

counterbored as at which advantageously has a conical bottom 20.

Fig. 7 is a top plan view of a different embodiment of the element shownin Fig. 6; and

Fig. 8 is a side elevation of the part shown in Fig 7.

Referring now to the drawing, the nut illustrated is of all metalconstruction embodying a nutbody III which may be of any desired metalsuch as iron or steel, brass, Monel, or one of the special lightermetals such as aluminum or magnesium, or alloys thereof. In theembodiment illustrated the nut body has been shown as having a'baseportion l2 of usual hexagonal form although it will be understood thatthe external shape or configuration of the nut may within the scope ofthe present invention be made of any form desired. The nut body isprovided with a differential bore comprising a portion I l passingthrough the base portion of the nutbody and IE to. provide a socket l8The nut body is further counterbored at the top of the nut, as at 22,the upper portion of the bore being defined by an annular wall or flange24 which as will be noted is of relatively narrow cross-section at itsupper part. The outer surface of the flange may advantageously bebeveled somewhat as indicated at 26.

In the embodiment illustrated the portion of' the nut body between thebore portions lli and 22 is formed to provide an annular axiallyextending flange 28 adjacent to the bore l6, between which flange andthe bore 22 there is an encircling annular recess 30.

A locking member indicated generally at 32 is provided which in thepresent embodiment is in the form of an annular washer-like inserthfaving a bore 34 of substantially the same diameter as the bore l4, adisc-like web portion 36, an

inner flange portion 38 depending from the web portion tion 40.

As will be observed from Fig. 1, this form of insert may be said to begenerally U-shaped in cross-section.

For reasons hereinafter more fully appearing, the disc portion 36 isrelatively very thin in crosssection axially of the nut and. because ofthe relatively very thincross-section required for this portion of thestructure, the insert is preferably in all cases made of non-corrodiblematerial such as stainless steel or the like, regardless of the materialof which the nut body is made. As will hereinafter more fully appear,stainless steel is particularly advantageous for other reasons in 36,and an outer depending flange porparts.

the manufacture of hardened nuts. It is essential to the properfunctioning of the nut that the material of the insert have asubstantial degree of elasticity and not be of any substantiallynonelastic material such for example as lead.

By way of example it has been found that when the insert is made ofpreferred material such as stainless steel or other material havingequivalent physical properties, particularly that of elasticity,satisfactory results are obtained when the web portion of the insert,which may for convenience be considered as the diaphragm portion, is ofthe order of from ten to fifteen thousandths of an inch thick for asmall nut of the order of 3 to V inch thread diameter. Four larger sizesof nuts this thickness of the diaphragm may be increased. the amount ofincrease of thickness depending upon the material of the diaphragm andthe size of the nut.

The nut body and the insert are separately formed by any suitablemachining operations and as will be. apparent from Fig. l, thesymmetrical nature of the shapes taken by these are such that they maybe finished to desired dimensions very rapidly and at low cost by manywell known types of automatic screw machines. After being suitablyformed to desired dimensions, the two parts are assembled in therelation shown in Fig. 1 with the U-shaped cross-section of the insertin inverted position, the flange part 40 of the insert fitting into therecess 30 of the nut body and the outer part of the diaphragm portionresting against the top of the annular flange "projecting upwardly inthe bore of the nut body.

In order for the finished nut to function properly, the insert must beretained against tuming movement in the nut body. This may beaccomplished in any desired and suitable manner. In the embodimentillustrated, the outer surface of the insert is knurled as indicated inFi 6, this knurled surface having a suillciently tight or locking fit inthe bore 22 of the nut body to prevent relative turning movement betweenthe two After the parts are assembled as shown in Fig. 1, the upperportion of the fiange 26 which extends above the top of the insert isbeaded over in any suitable manner, as by a spinning or pressingoperation, to form a lip 26a extending inwardly over the top of theouter part of .the insert. In some instances the axial pressure exertedon the insert by the lip may alone be relied on tolock the insertagainst turning movement in the nut body. In connection with thisoperation it is particularly to be noted that the radius of theinnermost point of contact between the lip 26:; and the insert, which inth embodiment illustrated is indicated by the radius n (Fig. 2), isgreater than the .radius r: of the inner-.

most point of contact between the nut body and the lower face of thediaphragm. For convenience in considering the action of the nut, thecircular line of' contact between the lip 26a and the insert, having theradius r1, may conveniently be considered as a first fulcrum establishedat a given radius, and the circular line of contact between the nut bodyand the lower surface of the diaphragm portion of the insert, having theradius r2, may be considered as a second fulcrum of different radius.Advantageously, theportion of the nut body forming this latter fulcrumis slightly rounded as indicated at 44 for reasons hereinafter appearingand the lower end surface 46 of the inner flange 38 of the insert isadvantageously beveled to an angle approximating the portion angle ofthe conical shoulder 20 at the bottom of the socket IS in the nut body.

After the parts of the nut are assembled as shown in Fig. 2, theassembly is then threaded to provide a thread 48 which is in the nature'of an interrupted thread the major section 48a of which is in the boreof the nut body and the minor section of which 481) is in the bore ofthe insert.

After the nut is threaded as shown in Fig. 3, the central "part of theinsert 32 is then deformed so that thediaphragm portion 36 is dishedtoward thebase of the nut. In this operation a part at least of themetal of the diaphragm portion of the insert is stressed beyond itselastic limit so that a permanent set in the metal occurs.

The dishing of the diaphragm toward the base of the nut will of coursedisplace the thread section 481) of the insert axially relative to thethread section 48a in the nut body and if the nut is to functionproperly the amount of this displacement must be such as to leave thetwo thread sections in out-of-phase relation to each other. In order tohave thesesections in outof-phase relation'it will be evident (assumingthe thread I threads made in accordance with usual commercial standards.The reason for this is that in order for the nut to function properly abolt threaded through the body of the nut must not be able to freelyenter the thread section of the insert.

' Particularly in the case of small nuts or nuts of any size having athread with a very fine pitch, the deforming operation must be carriedout with a' great deal of accuracy if it is reliably to be avoided thatthe thread of the insert after deforming is in phase or so nearly inphase with the thread section of the nut body that the bolt thread canfreely enter the thread section of the The punch 50 is provided with acircular shoulder .52 adapted to abut against the supported 1 outerportion of the diaphragm part of the insert to limit the downwardmovement of the punch relative to the nut. Inside the shoulder 52, thepunch is provided with a circular projection 54 which acts to depressthe central unsupported of the diaphragm part of the insert when thepunch is moved to the seated position shown in the figure.Advantageously, but not necessarily, the punch provided with a pilotportion 56 adapted to enter the bore of the insert in order to centerthe nut with respect to the projection 54 and insure deformation of thediaphragm of the insert concentrically with respect to the axis of thebore.

By utilizing a punch the movement of which relative to the nut isdefinitely limited by the seating of a shoulder against the uppersurface of the diaphragm of the insert,

central portion of the diaphragm is insured. In spite of the fact thatthe metal of the diaphragm is permanently distorted by the deformingoperation, the elastic nature of the material of the insert may resultin a slight tendency for the metal to return toward its originalposition and for this reason it may. in certain instances and dependingupon the speciflc nature of the metal of the insert, be desirable tomake the depth of the projection 54 of the punch slightly in excess ofthe flnal amount of axial displacement desired, so as to allow for suchtendency of the metal to return toward its original position as mayexist, while insuring the desired final extent of axial displacementafter the punch is withdrawn.

In order to permit the punch to displace the central portion of theinsert axially further than its finally desired position, and also to inany event insure seating of the shoulder of the punch against the uppersurface of the diaphragm, the length of the counterbore portion it ofthe nut body is made somewhat greater than the length of the dependingflange portion 38 of the insert so that a clearance space 8 is providedbetween the bottom surface of the insert and the bottom of the socketl8, which space has suflicient axial length to provide a remainingclearance space 81 after the insert is deformed.

The desired degree of axial displacement of the central portion of theinsert may also be secured by proportioning the parts so that the spaces has just sufllcient depth to permit the operation to be -eilected by astraight punch of the diameter of the projection 54 which will act toforce the bottom surface 46 of the insert into direct contact with thebottom of the socket, which contact furnishes the desired limiting stopforthe deforming operation. Even if the deforming operation is limitedby bottom contact, the elasticity of the material will ordinarily resultin a final clearance space .91 being formed after the deformingoperation is completed, due to the elastic material of the inserttending to reutrn toward its original position. It will be apparent thatfor different materials and different sizes of nuts the depth of thespace s will vary, but the and bring the upper thread flank of thethread section 48a into frictional contact with the lower flank of thebolt thread 50.

After the inner end of the bolt abuts against the lower end of theinsert, continued turning of the nut on the thread will cause the end ofthe bolt to deflect the diaphragm portion of the insert and lift thethread section 48b of the insert until the bolt thread can enter thisthread section. This action takes place against continuing resistance ofthe diaphragm to deflection from its set position so that the axialthrust on the bolt is continued after the nut is fully threaded onto thebolt, owing to the tendency ofthe insert to return to the position ofFig. 4. This axial thrust maintains constant friction not only betweenthe upper flank oi the thread section a and the lower flank of the boltthread 58, butalso between the lower flank of the thread section 48b ofthe insert and the upper flank of the bolt thread. Experience has provedthat if the flanksof several turns of thread can be maintained incontinuous frictional contact, such contact is suflicient to provideagainst turning of the nut relative to the bolt, even under the mostsevere conditions of vibration or shock.

In connection with the locking action afforded, it is also important tonote that the locking action is not dependent upon the base of the nutbeing drawn up against the surface of any object held thereby and it isfurther to be noted that if the nut is used in such a manner that it isdrawn up with its base in abutting contact with any object to be held bythe bolt and nut, the reactive pressure exerted by such object on thenut acts to produce axial thrust having the same direction betweenthebolt and the nut as that proper depth is very readily and easilydetermined by experiment in any particular case so that in the flnalposition assumed by the insert after the deforming operation, thedisplacement of the threads of the insert will result in the desiredout-of-phase relation of the two thread sections.

It is particularly to be noted in connection with the above describeddeforming operation that the deformation and the stressing of thematerial of the diaphragm beyond its elastic limit to a differentposition of permanent set takes place at the radius 12, or in otherwords about the fulcrum which appears as the point a: (Fig. 4). in thecross-section of the nut. This of course is due to the fact that outsidethe radius of the fulcrum point x, the metal of the insert is firmly andrigidly supported against downward movement by the nut body.

Turning now more particularly to Fig. 5,'the action of the nut is moreclearly apparent. As shown in this figure, the nut is threaded on acooperating bolt and it will be appreciated that as the bolt is threadedthrough the thread section a and into contact with the out-ofphasethread section 48b, the insert will exert an axial thrust on the bolt inthe direction of the arrow a which will take up any axial play in thethreads which is produced by the elastic locking part of the nut itself.The action is thus always the same whether the nut be used as a freeadjusting nut or as a clamping/nut.

In the nut structure embodying -the present invention it is particularlyto be noted that when the diaphragm is flexed upwardly by application ofthe nut to a bolt, the flexure takes place at radius T1 at the line ofcontact between the upper surface of the insert and the lip 26a, or, inother words, about fulcrum point 1 (Fig. 5) of any section. This featureis important for the reason that the flexure caused by. the applicationofthe nut to a bolt takes place in a section of the metal of the insertwhich has not previously been deformed beyond its elastic limit andwhich has not been previously overstressed. Thus the flexing of theinsert in service takes place in what may be termed previously unworkedmetal, which is much better able to withstand a large number of flexureswithout fatigue and consequent danger of failure than metal whichhaspreviously been worked, such as the metal which is bent over thefulcrum 1:.

Also it is to be noted that the radius 11 is relatively large ascompared with radius r For this reason the axial displacement of thethread section 48b by the original deforming operation can becompensated for by flexure around the radius n with much less angularbending movement of the metal around fulcrum 1/ than would be the caseif the restoring flexure took place also tends to add to the effectivelife of the nut under repeated flexures of the insert occasioned byremoval and reapplication of the nut to the same or different bolts,since the degree of flex ure required to enable the nut to be fullythreaded on the bolt may readily be kept well within the range ofelastic deflection of the metal.

The deforming or dishing of the diaphragm toward the base of the nutprovides another important feature of advantage in that as a result theholding power of' the nut is not impaired by rise in temperature but onthe contrary is enhanced by such rise. This makes it particularlysatisfactory for high temperature applications. This advantage isderived as follows: Upon increase in temperature of the nut the internaldiameter of the thread section 481) tends'to decrease due to expansion,and because of the characteristics peculiar to the construction of thenut, acts to increase the axial or locking thrust on the bolt relativeto the nut. The reason why decrease in diameter of the thread section bwill act to exert additional axial thrust is that after the nut isscrewed on a bolt, the diaphragm portion of the insert is still indished condition with the center of the insert depressed toward the baseof thenut so that any force exerted due to expansion of this dishedsection embodies a resultant axial component acting on the bolt in thedirection toward the base of the nut.

superficially it would appear that if the diaphragm is in a radial planeafter being threaded and before being deformed, and is subsequentlydeformed to bring the threads into the desired out-of-phase relation,that when the nut is threaded onto a bolt so that the two threadsections are again in phase relations because of being threaded onto thesame bolt thread, the diaphragm would necessarily be restored to itsoriginal radial position. This would be true if the threads on the boltand the nut were cut so that there would be no clearance whatsoeverbetween the flanks of the cooperating threads. Such a condition ishowever not obtained in the production of commercial nuts and bolts.Consequently, when the nut is threaded onto a bolt, the axial movementof the thread section of the insert toward its original position isequal to an amount corresponding to the degree of outof-phase relationof the thread sections, less the amount of clearance between the threadflanks. Since this clearance always exists, it will be evi-' dent thatthe insert remains in slightly dished condition even after the nut isthreaded onto a bolt and in this dished condition it will exert, if itexpands due to-heat, an axial thrust due to expansion, in addition tothe axial thrust exerted by the tendency of the flexed diaphragm toreturn to its permanent set position.

The insert need not necessarily be provided with an outer flange of thekind indicated at 40 in Fig. 1. such flange however aidingvin holdingthe insert against rotation in the nut body and also aiding in anadvantageous manner the desired rigid clamping of the outer periphery ofthe diaphragm in the nut body. The insert may be made in the form shownat 50 in Figs. 7 and 8,

in which the outer flange is omitted as well as the knurling of theouter surface, while the diaphragm portion is provided with a series ofperipheraly spaced notches 62 into which portions of the lip 26a, areforced when the lip is formed and which act as locking parts to preventturning of the insert.

Numerous important practical advantages are obtained by forming nutstructures in the manner above described.

Among such advantages the following are particularly to be noted.

By providing a socketed bore in the nut body into which the threadedsection of the insert is received, and retaining the insert in the nutbody by beading over the upper flange of the latter, the insert is fullyprotected against undesired displacements from accidental causes inshipment or handling. It will be appreciated that with the very thindiaphragm section which is employed, a comparatively light blow on thecentral section of the insert might be sufllcient to move it from itsproper position and even if the distortion from an accidental blow orthe like did not result in moving the thread section of the insert intophase relation with the remaining thread section, displacement of thethread section of the insert from the predetermined degree ofcut-of-phase relation would alter the amount of axial lockingthrustproduced by the nut. In nut structures of this kind it is highlydesirable that for any given size and kind of nut all nuts produce thesame degree of axial thrust and holding power. This may be particularlytrue in the case of nuts designed to be used with bolts of relativelysoft metal, as in such cases, too great an out-of-phase relationshipbetween the thread sections may result in sufficient axial thrust beingproduced when the nut is threaded on the bolt, to cause the bolt threadto be injured by the nut.

As previously noted, it is highly desirableto uniformly secure arelatively very exact out-ofphase relationship between the threadsections and it will be evident that the construction of nuts inaccordance with the present invention permits this to be done since theamount of deformation effected can be very accurately governed bydefinitely limiting the extent of the deforming operation'with anaccurately fixed abutment formed by part of the nut structure itself.

Nut structures according to the present invention are particularlyadvantageous for high temperature application, notonly because of theirI eflicient self-locking action at such temperature,

cause of the two piece construction which permits different metals to beemployed for the nut body and the insert, and also by the characteristicconstruction which permits advantageous use to be made of bi-metallicconstruction in the production .of hardened nuts.

As previously noted, non-corrodible metal such as stainless steel ornon-ferrous is advantageously employed for the inserts in order toeliminate the possibility of corrosion of the very thin section of thediaphragm. Another very important advantage lies in the possibility,contemplated as one of the features of this invention, of making theinsert of material which is not only noncorrodible in nature but whichis also non-hardening under thev conditions of heat treatment whichwould effect hardening of a steel nut body. One such metal is stainlesssteel.

In the manufacture of hardened nuts it will be evident that a steel nutbody can advantageously be formed and combined with a stainless steelinsert, to the form shown in Fig. 3, before the steel nut body ishardened. After the parts are assembled and threaded, with the steel inunhardened condition, the hardening and deforming operations can becarried out, it being immaterial which of these latter two operations isdone first. The hardening of the nut body after all machining operationshave been completed on it and with the insert locked in place, will notaifect the action of the nut since the temperatures required to hardenthe steel will not afiect the hardness or elastic proportions of thestainless steel insert. The same will be true if the insert is made ofbrass or other nonferrous, non-hardening metal.

The nut body cannot as a matter of commercial practicability be hardenedbefore the parts are assembled since the two parts must be in rigidlyassembled relation before being threaded, in order to insure initialin-phase relation of the thread sections and the final accuratelydetermined out-of-phase relationship of these sections. Moreover, if thenut body were hardened prior to assembly, the upper ,flange portion ofthe body would have to be subsequently drawn to soft condition to enablethe retaining lip 26a to be formed and such procedure is noteconomically practical.

It will be understood that for the purpose of making hardened nuts'awide variety ofsteels may be employed and hardened in different ways.

Thus high carbon and alloy steels which harden throughout when subjectedto proper heating and quenching operations may be employed, or lowcarbon steels may be employed which are subsequently hardened by any ofthe Well known methods involving carburizing and subsequent heattreatment to produce what is ordinarily referred to in the art as casehardened structure. As herein employed, the term harden and derivativesthereof are to be considered in their broad sense and not limited to anyspeciilc mode of hardening or type of hardened structure.

From the foregoing it will be appreciated that the inventioncontemplates within its scope methods of manufacture which may vary fromthe specific modes hereinbefore described by way of illustration, andthe invention is accordingly to be understood as embracing allvariations of methods falling within the scope of the appended claim.

What is claimed is: The method of making a self-locking nut whichincludes the steps of forming a metal nut body having a difierentialbore divided intothree portions of successively greater diameters fromthe base to the top of the nut and with said portions separated byshoulders, forming an annular insert of elastic metal having a centralportion relatively thick in. axial direction having an axially extendingbore therethrough and a relatively thin disc-like flexible diaphragmextending outwardly from said central portion, placing a said insert insaid nut body with the outer part only of the diaphragm supported by theshoulder between the two uppermost bore portions in the nut body,deforming the upper end wall of the nut body to provide a lip overlyingthe insert while maintaining the inner diameter of said lip reater thanthe inner diameter of the shoulder supporting said diaphragm, threadingthe portion of the bore in the base of the nut body and the bore portionof said insert to provide two coaxial thread sections and thereafterdeforming the insert by forcing the central bore portion thereof axiallytoward the base portion of the nut body until the central bore portionof the insert strikes the shoulder between the threaded bore portion ofthe nut body and the adjacent bore portion.

DANIEL C. HUNGERFORD.

